Bituminous-Materials - Mang Tia BITUMINOUS MATERIALS Mang...

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Mang Tia - 1 - BITUMINOUS MATERIALS Mang Tia, Professor of Civil and Coastal Engineering, University of Florida Introduction The term bituminous materials is generally used to denote substances in which bitumen is present or from which it can be derived [Goetz and Wood, 1960]. Bitumen is defined as an amorphous, black or dark-colored, (solid, semi-solid, or viscous) cementitious substance, composed principally of high molecular weight hydrocarbons, and soluble in carbon disulfide. For civil engineering applications, bituminous materials include primarily aphalts and tars . Asphalts may occur in nature (natural asphalts) or may be obtained from petroleum processing (petroleum asphalts). Tars do not occur in nature and are obtained as condensates in the processing of coal, petroleum, oil-shale, wood or other organic materials. Pitch is formed when a tar is partially distilled so that the volatile constituents have evaporated off from it. Bituminous mixtures are generally used to denote the combinations of bituminous materials (as binders), aggregates and additives. This chapter presents the basic principles and practices of the usage of bituminous materials in pavement construction. In recent years, the use of tars in highway construction has been very limited due to the concern with the possible emission of hazardous flumes when tars are heated. Thus, this chapter deals primarily with asphalts. Types of Bituminous Materials Used in Pavement Construction Asphalt cement is an asphalt which has been specially refined as to quality and consistency for direct use in the construction of asphalt pavements. An asphalt cement has to be heated to an appropriate high temperature in order to be fluid enough to be mixed and placed.
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Mang Tia - 2 - Cutback asphalt is a liquid asphalt which is a blend of asphalt and petroleum solvents (such as gasoline and kerosine). A cutback asphalt can be mixed and placed with little or no application of heat. After a cutback asphalt is applied and exposed to the atmosphere, the solvent will gradually evaporate, leaving the asphalt cement to perform its function as a binder. Emulsified asphalt (or asphalt emulsion ) is an emulsion of asphalt cement and water that contains a small amount of emulsifying agent. In a normal emulsified asphalt, the asphalt cement is in the form of minute globules in suspension in water. An emulsified asphalt can be mixed and applied without any application of heat. After an asphalt emulsion is applied, sufficient time is required for the emulsion to break and the water to evaporate to leave the asphalt cement to perform its function as a binder. In an inverted emulsified asphalt , minute globules of water are in suspension in a liquid asphalt, which is usually a cutback asphalt. Inverted asphalt emulsions are seldom used in pavement applications.
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This note was uploaded on 05/26/2011 for the course CGN 6505 taught by Professor Mang during the Spring '11 term at University of Florida.

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Bituminous-Materials - Mang Tia BITUMINOUS MATERIALS Mang...

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